More hypoxia incidents have occurred since the F-22 returned to the skies

The USAF's premiere air superiority fighter, the F-22 Raptor, had a rough year in 2011. There were several incidences of pilots exhibiting hypoxia-like symptoms that led to the aircraft being placed on stand-down for months while an investigation took place into the possible causes of the issue.

Fingers were pointed at the onboard oxygen generation systems and the OBOGS failure was thought to have contributed to the fatal crash of a Raptor pilot in 2010. That fatal crash was instead ruled pilot error.

On January 13, a report from the Pentagon's top tester was published on the grounding of the F-22 Raptors last year. According to the report, the Raptor stand-down last year was due to "suspected contamination problems with the aircraft environmental control system and associated onboard oxygen generation system from later April through late September 2011."

The report was penned by chief operational tester J. Michael Gilmore and confirms that toxins entering the cockpit of the F-22 had cause over twelve incidents that were similar to hypoxia. The USAF lifted the grounding before a hard answer to the cause of the problems was found. Since the grounding was lifted, the Raptors in the fleet have flown over 6,000 times. Defense News reports that more incidents of the hypoxia-like symptoms have occurred despite the precautions put into effect to install charcoal filters and have pilots wear pulse oximeters.

[Source: Lockheed Martin]

Air Force spokeswoman Jennifer Ferrau said, "There have been approximately 90 events of interest and 15 are being investigated for potential physiological incidents -- 8 involving pilots and 7 involving aircraft maintenance personnel. This translates to a 1.8 percent event rate since the return to flight in September."

In USAF parlance an "event of interest" is an indication of a malfunction in a system or a data point that has not caused hypoxia-like symptoms. A "physiological event" is one that has produced hypoxia symptoms.

Ferrau said, "Any event involving hypoxia-like symptoms may be categorized by Air Force Instructions as a physiological incident following an investigation."

Since the pilot is sitting inside the plane and not out in open air it's not sure an emergency dive for breathable air would have worked. Remember this is not about lack of oxygen in the breathing system but about all sort of gasses that should not be in the air feed to the pilot.